(a) Field of the Invention
The present invention relates to a keypad for a mobile phone and, more particularly, to a keypad that has a sheet-type luminous element (an EL element) formed in a thin sheet and integrated therein, thereby minimizing noise and vibration generated by the EL element.
(b) Description of the Related Art
Generally, a keypad for a mobile phone is an input device consisting of a separate grid of numerical and function keys arranged for efficient data entry. The keys are fitted into holes formed on a front housing of the mobile phones and jutted out so that users can conveniently input the data.
Light source formed of a luminous element is installed on the bottoms of the key so that the user can identify the numerical numbers and letters printed on the keys in a dark place. When the light source is turned on, the light is emitted to the letters and numerical numbers printed on the keys by the backlight effect, thereby making the users identify them.
FIG. 7 shows one of keys constituting a conventional keypad for a mobile phone.
A key 50 generally comprises a base 52, a key top 54 elevated from the base 52, and a projection 56 formed on a bottom center of the key top 54.
The base 52 and the key top 54 are integrally formed by a connecting portion 58. The connecting portion 58 is designed to be thinner than the base 52 for the effective operation of the key 50. A printing layer 60 of letters and numerical numbers is formed on a top surface of the key top 54 through a silkscreen printing or a laser marking.
The base 52 is provided at its bottom surface with a groove 62 in which a light source formed of an LED lamp is installed.
A dome switch 68 is located under the projection 56, and a fixed contact point 70 formed on a printed circuit board 64 is located under the dome switch 68.
When using the mobile phone, the light source 66 is applied with electric power to provide backlight to the keypad, making it possible to see the printing layer 60 with the letters and numerical numbers formed on the key top 54 even in the dark place.
When pushing the key 50, the projection 56 formed on the bottom of the key 50 overcomes the elastic formed of the dome switch 68 and pushes the dome switch 68 so that the dome switch 68 contacts the fixed contact point 70, thereby generating a signal.
When releasing the pushing force applied to the key 50, the key 50 is returned to its initial position by the self-elastic force of the connecting portion 58 and the dome switch.
However, in the conventional keypad, since a groove is formed on the bottom surface of the base 52 and the light source formed of the LED lamp is installed in the groove, the thickness of the keypad is increased as many as the thickness of the light source.
Furthermore, since the key 50, the dome switch 68, and the printed circuit board 64 are disposed in the front housing of the mobile phone, and a part of the key 50 is exposed out of the front housing, it is time consuming to assemble all of the members, thereby deteriorating the productivity.
To solve the above-described problem, a keypad for a communication device, which is provided with a sheet-type luminous element (an EL element) that is designed such that a spacer having opposite adhesive surfaces is attached on a circuit board and a backlight is provided on the spacer, has been proposed. However, a special assembling process for attaching the spacer is required, and the thickness of the keypad is increased as many as the thickness of the spacer.
Furthermore, a dome switch, a moving contact point, and a fixed contact point that are constituting the luminous element are not sealed, this causes the mobile phone's life to be reduce and also causes a shielding process for preventing the noise and vibration caused by current applied to the luminous element to be required.